I think if that's all buccaneers were, it wouldn't make sense for Oda to make them be a race. Because we already have large humans, like Big Mom, as well as normal giants. So why are human giant hybrids important enough to be a distinct race of their own?
Two things we can get from Saturn's words.
Moving on, it seems as if the world government might actually be afraid of the Buccaneer race.
Merely having buccaneer blood is enough for one to be enslaved. This is in grave contrast to the Ds, who while also being descendants of people who rebelled against the WG, don't actually seem to be persecuted in the OP world. This can be seen with Saul and Garp, both of whom were high ranking marines despite their D heritage. I think this also refutes the idea that Buccaneers are special solely because they know about Nika. Because if this was true, then a blood test alone wouldn't be enough to cause their enslavement. The fact that they are enslaved due to their blood means that there must be something special about buccaneer physiology itself that the WG fears.
This makes sense because when we look at other races that have been annihilated. Ones that come to mind are the 3 eye tribe and the lunarians, both who also seem to be near extinct. In both cases, you have races that have abilities that the WG fears. Lunarians have their near invincibility and 3 eyes are said to be able to read poneglyphs once their 3rd eye awakens.
So what is special about the blood of a buccaneer? well if they are descended from a people who made a grave sin against the world, I think we have a decent idea of who these people might be related to.
They are probably from the same tribe as Joyboy, as evidenced by the giant straw hat in Imu's freezer.
From this, I think that there is a very high chance that the reason why the WG fears them so much is because:
It wasn't enough for Kuma to simply become a Shichibukai, an ally of the WG. No, Saturn wanted to completely erase his consciousness. Why is this? Well if buccaneers really do have a strong talent for haki or VOAT, this would make perfect sense. After all, if Kuma has his consciousness, he might eventually become unstoppably powerful due to the haki talent buccaneers have.
Ultimately, I think we will see this talent first hand with S-Bear. The seraphim have some consciousness and hence its possible that they could eventually develop haki. I see Oda giving these abilities to S-Bear in order to emphasize the powers of a buccaneer and show what Kuma could have been if he wasn't handicapped by the WG.

Two things we can get from Saturn's words.
- Buccaneers aren't just any large humans, they are specific lineage of people who committed a grave sin against the world
- Kuma was the last of this race.
Moving on, it seems as if the world government might actually be afraid of the Buccaneer race.

Merely having buccaneer blood is enough for one to be enslaved. This is in grave contrast to the Ds, who while also being descendants of people who rebelled against the WG, don't actually seem to be persecuted in the OP world. This can be seen with Saul and Garp, both of whom were high ranking marines despite their D heritage. I think this also refutes the idea that Buccaneers are special solely because they know about Nika. Because if this was true, then a blood test alone wouldn't be enough to cause their enslavement. The fact that they are enslaved due to their blood means that there must be something special about buccaneer physiology itself that the WG fears.
This makes sense because when we look at other races that have been annihilated. Ones that come to mind are the 3 eye tribe and the lunarians, both who also seem to be near extinct. In both cases, you have races that have abilities that the WG fears. Lunarians have their near invincibility and 3 eyes are said to be able to read poneglyphs once their 3rd eye awakens.
So what is special about the blood of a buccaneer? well if they are descended from a people who made a grave sin against the world, I think we have a decent idea of who these people might be related to.

They are probably from the same tribe as Joyboy, as evidenced by the giant straw hat in Imu's freezer.
From this, I think that there is a very high chance that the reason why the WG fears them so much is because:
- They have a high potential with haki
- They possess VOAT

It wasn't enough for Kuma to simply become a Shichibukai, an ally of the WG. No, Saturn wanted to completely erase his consciousness. Why is this? Well if buccaneers really do have a strong talent for haki or VOAT, this would make perfect sense. After all, if Kuma has his consciousness, he might eventually become unstoppably powerful due to the haki talent buccaneers have.
Ultimately, I think we will see this talent first hand with S-Bear. The seraphim have some consciousness and hence its possible that they could eventually develop haki. I see Oda giving these abilities to S-Bear in order to emphasize the powers of a buccaneer and show what Kuma could have been if he wasn't handicapped by the WG.